Heat exchangers are known, for example to be used as radiators in cooling circuits of motor vehicle engines, which comprise a nest of finned tubes through which flows the engine cooling fluid and at least a collector formed of a plate with holes into which are engaged and tightly fitted the tube ends. To said plate is joined a water box which may comprise at least one fluid inlet or outlet pipe and which is attached to the plate via its edges, particularly by means of lugs or of bent flanges of said plate.